The invention relates to a high-pressure discharge lamp which is provided with a discharge vessel that encloses a discharge space and includes a ceramic wall, the discharge space accommodating an electrode which is connected to an electric current conductor by means of a leadthrough element. The invention also relates to a high intensity discharge (HID) lamp having a discharge vessel light source, a glass stem, a pair of leads embedded in the glass stem, a glass envelope surrounding the light source, and a wire frame member with a first end fixed with respect to the stem, an axial portion extending parallel to the axis of the lamp, and a second end resiliently fitted in the closed end of the glass envelope.
High intensity discharge (HID) lamps are commonly used in large area lighting applications, due to their high energy efficiency and superb long life. The existing HID product range consists of mercury vapor (MV), high pressure sodium (HPS), and quartz metal halide (MH) lamps. In recent years, ceramic metal halide lamps (for example, Philips MasterColor(copyright) series) have entered the market place. Compared to the conventional HID lamps, the ceramic metal halide lamps display excellent initial color consistency, superb stability over life (lumen maintenance  greater than 80%, color temperature shift  less than 200K at 10,000 hrs), high luminous efficacy of  greater than 90 lumens/watt and a lifetime of about 20,000 hours. These highly desirable characteristics are due to the high stability of the polycrystalline alumina (PCA) envelopes and a special mixture of salts, which emits a continuous-spectrum light radiation close to natural light.
The salt mixture used in Philips MasterColor(copyright) series lamps is composed of NaI, CaI2, TlI, and rare-earth halides of DyI3, HoI3 and TmI3. NaI, CaI2 and TlI are mainly for emitting high intensity line radiation at various colors, but they also contribute to continuous radiation. The rare-earth halides are for continuous radiation throughout the visible range, resulting in a high color rendering index (CRI). By adjusting the composition of the salts, color temperatures of 3800-4500K, and a CRI of above 85 can be achieved. The existing power range of such lamps is from 20 W to 150 W. The relatively narrow power range makes these products only suitable for the applications requiring low power installations, such as most indoor low-ceiling retail spaces. For large area, higher power applications requiring a lamp power of 200 W to 1000 W, the primary available products are MV, HPS and MH lamps.
One example of a lamp of the kind set forth is known from U.S. Pat. No. 5,424,609. The known lamp has a comparatively low power of 150 W at the most at an arc voltage of approximately 90 V. Because the electrode in such a lamp conducts comparatively small currents during operation of the lamp, the dimensions of the electrode may remain comparatively small so that a comparatively small internal diameter of the projecting plug suffices. In the case of a lamp having a rated power in excess of 150 W, or a substantially lower arc voltage, for example as in the case of large electrode currents, electrodes of larger dimensions are required. Consequently, the internal plug diameter will be larger accordingly. It has been found that in such lamps there is an increased risk of premature failure, for example due to breaking off of the electrode or cracking of the plug.
There is a need in the art for HID lamps of the ceramic metal halide type with power ranges of about 150 W to about 1000 W.
An object of the invention is to provide HID lamps of the ceramic metal halide type with power ranges of about 150 W to about 1000 W. The nominal lamp voltage, as specified by applicable ANSI standards for HPS and MH varies from 100V to 135 V for 150 W to 400 W lamps and then increases with the rated power to about 260V for 1000 W lamps.
Another object of the invention is to provide ceramic metal halide lamps of the Philips MasterColor(copyright) series that display excellent initial color consistency, superb stability over life (lumen maintenance  greater than 80%, color temperature shift  less than 200K at 10,000 hrs), high luminous efficacy of  greater than 90 lumens/watt, a lifetime of about 20,000 hours, and power ranges of about 150 W to about 1000 W.
Another object is to provide a way to mitigate the drawbacks and risks of failure discussed above.
These and other objects of the invention are accomplished, according to a first embodiment of the invention in which an entire product family of gas discharge lamps with rated power of 150 W to 1000 W are provided which may be coupled with ANSI standard series of ballasts designed for high pressure sodium or quartz metal halide lamps (pulse-start or switch-start). The lamps of the invention are an extension of Philips MasterColor(copyright) series lamps to a power range of 150 W to 1000 W, and they are suitable for same-power HPS or MH retrofit. Therefore, they may be used with most existing ballast and fixture systems.
In its preferred embodiments, the invention provides ceramic metal halide lamps having a power range of about 150 W to about 1000 W, suitable for high pressure sodium and/or quartz metal halide retrofit.
In another preferred embodiment, such high power lamps as described above will have one or more and most preferably all of the following properties: a CCT (correlated color temperature) of about 3800 to about 4500K, a CRI (color rendering index) of about 70 to about 95, a MPCD (mean perceptible color difference) of about xc2x110, and a luminous efficacy up to about 85-95 lumens/watt.
In another preferred embodiment, ceramic metal halide lamps are provided which have been found, regardless of the rated power, to have a lumen maintenance of  greater than 80%, color temperature shift  less than 200K from 100 to 8000 hours, and lifetime of about 10,000 to about 25,000 hours.
Especially preferred are ceramic metal halide lamps that display excellent initial color consistency, superb stability over life (lumen maintenance  greater than 80%, color temperature shift  less than 200K at 10,000 hrs), high luminous efficacy of  greater than 90 lumens/watt, a lifetime of about 20,000 hours, and power ranges of about 150 W to about 1000 W.
The invention also provides novel design spaces containing parameters for any lamp power between about 150 W and 1000 W in which appropriate parameters for the body design of a lamp operable at the desired power is obtained by selection from parameters in which (i) the arc tube length, diameter and wall thickness limits are correlated to and expressed as functions of lamp power, and/or color temperature, and/or lamp voltage, and (ii) the electrode feedthrough structure used to conduct electrical currents with minimized thermal stress on the arc tube are correlated to and expressed as a function of lamp current. The invention also provides methods for producing ceramic metal halide lamps having predetermined properties through use of the design spaces of the invention.